The perpetrators were among a large crowd of men of reportedly Arab or north African backgrounds who gathered around the train station, drinking and discharging fireworks.

Politicians and police have been pointing the finger of blame at one another – while the racially charged character of the events has poured fuel on the fire of an already tense debate over the number of refugees in Germany.

While there is no evidence that any of the perpetrators were refugees, conservatives and the far-right have gladly built the attacks into complaints over the large numbers of Muslims who have arrived in Germany seeking asylum since summer 2015.

Organizers in the group posted that they planned to "patrol through the city" to help women if they saw them under attack.

They said that the group was not political or violent, but had simply formed to make the city "safer for our women".

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Around 1,000 people had joined the group, which plans its first outing on Saturday, after it had existed for just one day.

"The police are responsible for public security in Germany," a city police spokesman told RP. "Going in search of criminals in a conscientious and targeted way is not the business of ordinary citizens."